Spark plug and method of making the same



Nov. 9, 1943.

T. TOGNOLA SPARK PLUG AND METHOD OF MAKING TH, SAME Filed Jan. 3l

ERS EMBEDDED IN PHOSPHATE HAVING A HIGH MELTING POINT INVENTOR 72u@ Ty@ ATTORNEYA in an engine cylinder (not shown).

PatentedfNov. 9, 1943 SPARK PLUG AND METHOD OF MAKING THE SAME Tullio Tognola,Sidney, N. Y.,

assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation o t Delaware f Application January 31, 1941, Serial No. 376,725 z claims. (c1. 12s- 169) This invention relates to ignition apparatus. and more particularly to spark plugs for use in internal combustion engines or the like and to the art of making said spark plugs.

One of the objects of the present invention is to provide a novelly constructed spark plug for use in the ignition system of an internal combustion engine.

Another object of the invention is to provide a spark plug 'embodying novel sealing means for preventing the leakage of gases between the various parts thereof.

A further and important object of the inveny Y tion is to provide 'a novel method of constructing a spark plug of the above character.

A still further object is to provide a novel spark plug wherein the deleterious effects of high temperatures and gas leakage are reduced to a minimum.

VAnother object is to provide a spark plug incorporating a novel sealing substance that will not carbonize or deteriorate at the high temperatures to which the plug is subjected during use.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood. however, that the drawing is for the purpose of illustration only and is not intended as a deiinition ofthe limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawing, wherein views,

like reference char- V acters refer to like parts throughout the several derstood in the art is pering at 1, whichmay be of any suitable type known in the art, and is secured in place in any well-known manner, such as by silver solder.

In spark gap relation with ground electrode 1 for cooperation therewith in a manner well unthe head portion 8 of a center electrode 9. The elongated stem lll of said center electrode is surrounded by a metallic sleeve Il of copper or like material, said stem prefer-A ably having a drive fit therein. For a novel purpose to hereinafter appear, the upper end of sleeve or tube ll is externally reduced as by ta- I2, and an annular external groove I3 is provided therein at a short distance below the end of the taper.

Surrounding tube I I is a sleeve I4 of high heat resisting electrical insulation, such as`mica. As shown, said insulating sleeve consists of a plurality of layers of sheet mica and has a closeof mica washers 20, said washers extending from a shoulder 2| to aplane adjacent the upper end of stem l0. The entire center electrode or core form of radio-shielded spark plug made in ac cordance with the present invention;

2 is a. bottom view of the spark plug of lg- Z Fig. 3 is a detail sectional view, with parts broken away yand on an enlarged scale, showing a central portion of the spark plug of Fig. 1; and, Fig. 4 is a detail view, with parts broken away, showing loosely assembled parts of the center electrode or core assembly during one phase of the fabrication of the spark plug of Fig. 1.

The single embodiment of the invention illustrated in the drawing, by way of example, comprises a tubular body 5 which is externally threaded at '6 for cooperation with a threaded opening Mounted in the lower end of body 5 is a ground electrode assembly is clamped' together to form a unitary structure with washers IB and 20 under compression by means of ametallic washer 22. The

latter surrounds the upper end of stem I0 in engagement with the upper surface of stack 20 and is secured in positionby rolling or riveting the upper recessed end of said stein outwardly into engagement with the outer face thereof as indicated at 23.

If a radio-shielded spark plug is desired, a shielding barrel 24 may be secured to or formed integrally with nut I6 and extend upwardly therefrom beyond the outer end for connection in any well-known manner to the shielding for a high tension supply cable. Barrel 24 is preferably lined with an insulating sleeve 25 which may be of sheet mica and has a close sliding fit with'the outer surface of' mica stack 2D.` Liner 25 is protected Vat its upper end by a metallic ring 26 secured in thel upper end of barrel 24, Ring 26 may havel a pressent in barrel 24 or may be secured in positin by silver soldering, by rolling the upper edge of barrel 24 o'f center electrode 9' .indicated in Fig. 1, but attention ject to as high temperatures into Contact therewith, or by any other suitable means. It will be understood, of course, that the invention is not limited to a radio-shielded plug but may be incorporated in non-shielded plugs as well.

Novel means are provided for filling the minute spaces between various parts of the central electrode assembly to thereby minimize gas leakage through the spark plug from the engine cylinder and, hence, substantially eliminate ilashovers between the center electrode yand core nut I6. At the lower or inner end of the spark plug, which portion is subjected to the highest temperaturesl durin-g use, the minute spaces which necessarily occur between washers A in the upper portion of stack I8 and between said Washers, sleeve I4 and nut I6 are filled with a novel sealing material in accordance with a novel method to be hereinafter described. Said material consists of a metaphosphate, such as may be derived by dehydrating sodium phosphate, calcium phosphate or barium phosphate. Because of the small scale employed in the drawing, this lling material cannot with any degree of accuracy be is invited thereto by a suitable legend on the drawing. Filling or sealing materials of theiabove character have melting points ranging approximately from 1140 F. to 1780 F. and accordingly adequately resist the high temperatures to which the lower portion of the spark plug is subjected during use in present day engines. Additionally, said lling materials form .solids upon cooling from melted form and constitute an excellent seal against gas leakage and the accumulation, in the spaces between the mica insulation, of gases which may become ionized and form a conductive path for electrical current between electrode head 8 and nut I6. By thus preventing ashovers and gas leakage, any carbonization of the mica insulation which results in an electrically conductive path is substantially prevented. Since the dehydrated or metaphosphate ller may at a temperature near its fusing point become a conductor of electricity, although an extremely poor one, only the upper portion A of the Washer stack I8 is treated therewith. In addition to the above-mentioned filling materials, potassium metaphosphate, strontium metaphosphate, and possibly others might also be used.

Although the washers 2,8 may also be treated with the above materials, particularly when the plug is not of the shielded type, the upper portion of the center electrode assembly is not subas the lower portion thereof whichhas direct contact with ,the gases of combustion in the engine cylinder. Gas leakage and ashovers may `accordingly be prevented through this portion of the plug by means of a ller 21, the heat resisting -abilities of which may be somewhat less than the phosphate ller above described. Filling material 21 is placed in the plugin a manner to be hereinafter described so that it will fill substantially Aall the spaces between parts II, I4, 20v and 25 above shoulder 2|, thereby preventing leakage 0f gases from the engine cylinder and pockets in the insulating material which might enhance the possibility of ashovers. One material which has been found suitable for use as ller 21. is made from Cashew nut-shell oil in accordance with the teachings oi. U. s. `patents issued to Mortimer T. Harvey. One preferred material of this 'character is obtained by taking the undistillable part of raw cashew nut-shell preferably eliminating air.

CTI

y ture of approximately 1300 oil, such as the residue obtained in roilowing the teachings of U. S. Patent No. 2,157,126, and polymerizing the same under acid conditions, such as with sulphuric acid, in the manner disclosed in U. S. Patent No. 2,128,247. A small percentage of xylol or other suitable 4solvent or thinning agent may be added to the resin thus obtained to produce the desired viscosity. The resin or compound may be placed in the plug in liquid form, a. viscosity comparable to that of 250 S. A. E. oil being suitable. If linseed oil is used as a thinner, the desired viscosity and properties may be obtained by adding about 45% to 55% linseed oil to the resin. This liquid compound may be set by properoaking after it is incorporated in the spark plug without appreciable shrinkage to form a relatively hard, yet pliable and yieldable substance, which is an excellent insulator and capable of resisting the high temperatures to which the upper portion of the spark plug is subjected.

In the novel method of fabricating the abovedescribed spark plug, copper tube II is first pressed onto spindle or stem IIJ, a good press nt being required in order to prevent gas leakage. Said tube is then provided with taper I2 and groove I3. Sufficient sheet mica is then Wrapped tightly around tube II to provide a close sliding t through the central bore of nut I6. If desired, a small amount of filler 21 in a viscous liquid form may be placed between the layers of sleeve I4 adjacent the upper end thereof. Mica washers I8 are then placed on sleeve II, the Washers in portion B of the stack being of the exact diameter and thickness for lling recess I8, and the washers in portion C of the stack having a somewhat greater diameter, as indicated in Fig. 4, to permit subsequent machining thereof.

The above sub-assembly is inserted part way into nut I6, as seen in Fig. 4, and filling material 28 in the form of powdered sodium metaphosphate, for example, mixed with suflcient monobasic sodium phosphate in liquid form to make a thick paste, is placed in a groove 29 forment by dividing and separating recess washers Filling compound 28 is then melted by applying` a llame directly thereto, preferably while the electrode sub-assembly is rotated in a suitable xture at approximately R.. P. M. The melted nlllng material flows along mica. sleeve I4 and between the mica washers I8 adjacent groove 29. The time required for the melting operation varies with the heating means employed and the particular type of metaphosphate used as the filling ,material., During the melting operation, when sodium phosphate is employed, it 'is desirable that the washers B be heated to a tempera- F. and that the lower portion of nut I6 reach a temperature of around 600 F. In-some instances phosphoric acid may be used as one of the paste making ingredients.

While` the sub-assembly of the spark plug is still under the llame, or immediately after it is removed, pressure is applied to force `the spindle assembly, consisting of the central electrode and sleeves II and I4, into nut I84and to compress washers I8, a total pressure of about 500 lbs. being adequate in most cases. Upon the application of pressure, the excess lling compound 28 is squeezed out around the end of nut I6. Before the pressure is released, the parts should be clamped in compressed 'position by some suitable clamping means. When the heated subassembly has cooled to about F., it may -be f groove serves as a sort of reservoir -cess compound may accumulate.

removed from the clamping fixture and then baked in an oven at about 250 F. for several hours in order to dry the same.

After the assembly is removed from the oven. the mica washers 20 of the upper stack are coated with cashew nut-shell oil compound 21 in liquid form. and inserted in'barrel 24. Washer 22 with the lower face thereof smeared with compound 21 is then placed in position and pressure is applied to compress stack 20. During the application of presure, the upper end of stem I is pressed or riveted outwardly to secure the entire electrode assembly in compressed assembled relation. During the riveting of the upper end of stem III, head 8 of the center electrode should rest on la solid support in order to insure against breaking of the seal provided by fillingmaterial 28 .and to insure proper compression of washer stacks I8 and 20.

During. the compression of' washers 20, excess compound applied to the same is squeezed out, thereby completely filling the annular spaces between said washers and sleeves I4 and 25. The filling material on the lower face of washer 22 is sufficient t0A slightly more than ll the space created by taper I2 on tube II, and said tapered portion is adapted to direct material 21, when pressure is applied, to the minute annular space 30 between sleeve Il and tube I I, said space being magnified in Fig. 3 for purposes of illustration. In order to prevent lling material 21 from being pressed down into the hotter portion of the plug where it might be deteriorated by heat and, hence, become electrically conductive, groove I3 is provided in the outer surface of tube II. This in which exlling compound 21 may also iind its lway from the upper edge of sleeve I4 to any spaces which occur between the various layers thereof. The completed sub-assembly is now placed in an oven and baked for several days from temperatures rangingr from 200 F. to. 500 F. to cause the ller 21 to properly set and become a solid. Thereafter, the central electrode assemblyis machined to size and inserted in body-5. 4

There is thus provided a novel spark plug which has novel sealing means incorporated therein for preventing gas leakage and undesired flashovers or arcing, thereby enhancing the life and eiliciency of the plug. Said sealing means comprises materials which have not been heretofore used in the manufacture of spark plugs and which have extremely good heat resisting qualities. A

novel method for fabricating said spark plug and particularly forincorporating said sealing means therein is also provided. 4'Ihe spark plugthus provided4 has better physical and electrical characteristics than any similar plugs heretofore known, the. sealing means being relatively unaffected by expansion .and contraction of the parts of the plug during use thereof in an en Although only a single embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the in- -vention is not limited thereto. For example, the

novel sealing means may be incorporated in spark plugs of speciiically difiere t construction and the novel method may also be practiced in connection with spark plugs which differ in some respects from the one illustrated.` Various other changes may also be made in the design and arrangement of parts illustrated aswell as in the specific materials mentioned by way of example without departing from the spirit and scope of the Some of the invention as the same will now be understood by those skilled-in the art. For a deiinition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

l. In a spark plug, a center electrode, electrical insulation surrounding said electrode, a. me-kv tallic body member surrounding said insulation, and a quantity of dehydrated mono-basic phosphate filling spaces between said insulation and said member.

2. In a spark plug, a metallic body member having a bore therein, an electrode extending into said bore, electrical insulating means interposed between said member and said electrode, and sealing means including a quantity of solidified metaphosphate associated with said insulating means.

In a spark p1ug,a metallic body member, a center electrode in said member, electrical insulating means interposed between said memberand electrode, said insulating means including a stack of washers, at least a portion of said stack of washers being embedded in a quantity of solidied metaphosphate. e

4. In a spark plug, a metallic body member, a center electrode in said member, electrical insulating means interposed between said member and electrode, said insulating means including a stack of washers, and means including a solidified metaphosphate for unifying at least a portion of said stack of washers. t

.5. In a. spark plug, a metallic body '.member having a differential bore therein, a center electrode extending into ing means interposed between said member and electrode, said insulating means including a stack of washers, some of which washers are positioned in said bore. and a solidified, dehydrated monobasic phosphate lling the space between said member and the Washers in said bore.

6. A spark plug comprising a plurality of assembled parts including a metallic body member` having a bore therethrough, an electrode extending into said bore and electrical insulation interposed between said member and electrode, and sealing means consisting of a quantity of solidified metaphosphate filling spaces between said insulating means and another of said parts.

7. A spark plug corrlprsingI a plurality of assembled parts including a metallic body member having a bore therethrough, a center electrode extending into said bore and electrical insulation interposed between said member and electrode. and sealing means consisting of sodium metaphosphate lling spaces between said insulating means and another of said parts.

8. A spark plug comprising a plurality of assembled parts including a metallic body member having a bore therethrough, a center electrode extending into said bore and electrical Vinsulation interposedbetween said member and electrode, and sealing means consisting of calcium metaphosphate illling spaces between said insulating7 means and another of said parts.

9. A spark plug comprising a plurality of as-4 sembled parts including a metallic body member having Aa bore therethrough, a center electrode extending into said bore and electrical insulation interposed between said member and electrode. and sealing means consisting of barium meta- Aphosphate'lling spaces between said insulating posed in the bore ofk said member, means for insaid bor'e. electrical insulat- `sembly comprising a center electrode having an elongated stem, a metallic tube closely surrounding said stem, the outer surface of said 4tube-at the upper end thereof being tapered, an electrical insulating sleeve sui rounding said tube, whereby an annular tapered space is` formed between said tube and sleeve, and a solidified electrical insulating material filling the space between said tube and sleeve from theupper ends thereof to a plane below the tapered portion of said tube.

12. In a spark plug, a centerelectrode assembly comprising a center electrode having a reducedy tapered portion adjacent the upper end thereof, a cylindrical electrical insulating sleeve surrounding said electrode, whereby an annular tapered space is formed between said electrode and sleeve, and a solidified insulating material filling the space between said electrode and sleeve from the upper end of said sleeve to a plane below the tapered portion of said electrode.

13. In a spark plug, a center electrode assembly comprising a center electrode having a reduced tapered portion adjacent the upper end thereof and an annular external groove below said tapered portion, a cylindrical electrical insulating sleeve surrounding said electrode, 'and a filler of electrical insulating material filling the space between said sleeve and electrode above said groove.

14. The method of making a spark plug which comprises the steps of loosely assembling a body member, a center electrode, and means for. electrically insulating said electrode from said body member, applying a quantity of substantially dehydrated monobasic phosphate having a consistency of paste tothe aforesaid assembled parts, subjecting said phosphate to the action of a llame` to melt the same, and pressing said assembled parts together while said phosphate is in melted condition.

15. The method of making a spark plug which comprises the steps of loosely assembling a body member, an electrode, and means for electrically insulating said electrode from said member, placing a mixture'of nmetaphosphate and monobasic phosphate on the aforesaid assembled parts, applying heat locally to melt said mixture and reduce the same to metaphosphate form, pressing said assembled. parts together while saidmetaphosphate is in a melted condition, maintaining said parts in compressed condition while permitting said met'aphosphate to solidify, and baking said assembled parts to dry said metaphos- Dhate. l n

16. The method of making a spark plug which comprises the steps ofassembling a body member, a. center electrode, and means for electrically insulating said electrode from said body member including-a stack of insulating washers interposed loosely between said body member and an enlarged portion of said electrode, applying a quantity o1' metaphosphate intermediate the ends of said stack, melting said metaphosphate by apping a flame directly thereto, compressing said st k while said metaphosphate is in melted condition, and maintaining the compression pressure while said metaphosphate solidifies.

meta form.

18. AThe method of making a spark plug which comprises the steps 'of loosely assembling a body member, an electrode and means for electrically insulating said electrode from said member, melting a quantity of phosphate in its meta form on the assembly, pressing the parts of said assembly into fully assembled relation while said phosphate isimmelted condition, and maintaining said parts under pressure until said phosphate solidies.

19. In a spark plug,`a metallic body having a bore therein, an electrode extending into said bore, and electrical insulating means interposed between said member and said electrode, said means comprising a quantity of solidified metaphosphate.

20. The method of making a spark plug which comprises the steps of loosely assembling a body, a center electrode and means for electrically insulating said electrode from said' body, applying a quantity of metaphosphate to at least some of I the aforesaid assembled parts, heating said metaphosphate to render the same flowable, and pressing said parts into final assembled position while said metaphosphate is in a owable condition.

21. The method of making a spark plug which comprises the steps of assembling a body member, a center electrode and means for electrically insulating said electrode from said body member, and causing a quantity of metaphosphate in a flowable condition to flow into minute spaces between said insulating means and at least one of the other assembled Darts.

22. The method of making a spark plug which comprises a body member, al center electrode and means for electrically insulating said electrode from said body which includes the steps of causing a quantity of metaphosphate in a fiowable condition to flow into spaces between at least some of the aforesaid parts, and causing said metaphosphate to solidify while said parts are held in assembled relation.

23. The method of making a spark plug com- Drising a body member, a center electrode and means including a stack of insulating washers for electrically insulating said electrode from said body which includes the steps of applying a quantity of metaphosphate intermediate the ends of said stack, heating 'said metaphosphate for reducing the same to a flowable condition, compressing-said stack while said metaphosphate is in a fiowable condition, and maintaining the compression pressure while said metaphosphate solidies.

24. In apparatus of the class described, elongated electrical conducting means and electrical insulating means surrounding at least a. portion of said conducting means, said insulating means including a stack of insulating -washers embedded in a quantity of solidified metaphosphate;

25. The method which/"includes the steps of assembling electrical insulating means around electrical conducting means, causing a quantity of metaphosphate in a flowable condition to now into the minute spaces in said assembly, and causing said metaphosphate to solidify for sealing said spaces.

TULLIO TOGNOLA. 

